The invention relates to an apparatus for operating a resolver which includes at least one first receiver winding and at least one excitation winding, which are/can be associated with a rotor, and an evaluation device, which determines an angular position as a function of a voltage induced by means of the excitation winding through the rotor into the receiver winding.
In addition, the invention relates to a resolver device including a resolver and the apparatus described above as well as to a method for operating such a resolver device.
A so-called resolver is also frequently used in the automotive field in order to detect the angular position of a rotor of an electrical machine. The resolver constitutes an electromagnetic measuring transducer which outputs an electrical variable, for example voltage, as a function of the angular position. To this end, the resolver typically has a housing, in which two receiver windings that are offset by 90° to one another are disposed, said receiver windings enclosing a rotatably mounted rotor in the housing. At least one excitation winding is furthermore associated with the rotor and can, for example, be electrically contacted by means of a slip ring system. Resolvers are, however, also known which operate without brushes and therefore inductively transmit information to the excitation winding. The rotor is thereby expediently connected to an output shaft of the electrical machine or is directly formed by said shaft. Different electrical signals are generated as a function of the angular position of the rotor to the receiver windings by means of induction. To this end, the receiver windings are excited by a sinusoidal AC voltage, wherein the first receiver winding is excited by an AC voltage that is shifted by 90° with respect to the second receiver winding. The phasing of the voltages induced in the receiver windings thus depends on the position or, respectively, angular position of the rotor. Different resolver designs are generally known. Resolvers are also known, in which the excitation winding is disposed on the rotor such that it can rotate with said rotor and is, for example, contacted by means of the aforementioned slip ring system. If the rotor is located exactly at the angular position of 0° or 180°, a voltage of 0V results at the first receiver winding (referred to as sine winding). If the rotor is located exactly at the angular position of 90° or 270°, a voltage of 0V results at the second receiver winding (referred to as cosine winding). When the electrical machine is at rest at an angle of 0° or 180°, a short circuit bypassing the first stator winding can therefore not be detected. In the case of the sine track, a short circuit in the windings cannot be distinguished from an intact resolver at an angular position of 0°. Accordingly, a short circuit in the cosine track cannot be detected at an angular position of 90° and 270°. In other resolver designs, the exciter winding as well as the receiver windings is fixedly disposed relative to the housing or, respectively, on the stator side, wherein the exciter winding generates a magnetic field in the rotor by means of induction, which in turn induces a voltage in the receiver windings. In so doing, the coupling in the receiver windings is correspondingly dependent on the position of the rotor, wherein a maximum coupling into the cosine track occurs accordingly at an angular position of 0°.